1. Field of the Invention
The present invention relates generally to a communication system, and more particularly, to a method and apparatus for transmitting and receiving uplink control information.
2. Description of the Related Art
Intensive research is being conducted in the field of mobile communication systems on Orthogonal Frequency Division Multiplexing (OFDM), which is a scheme useful for high-speed data transmission in radio channels, and/or on Single Carrier—Frequency Division Multiple Access (SC-FDMA), which is a scheme similar thereto. In 3rd Generation Partnership Project (3GPP), which is the asynchronous cellular mobile communication standard group, a study of a Long Term Evolution (LTE) system, which is the next generation mobile communication system, is being conducted based on the foregoing multiple access schemes.
In the LTE system, the term ‘uplink Channel Quality Indicator (CQI) information’ refers to channel quality-related information of a downlink, which is fed back from a terminal(s) to schedule downlink resources. CQI information necessary for scheduling may include:                Wideband CQI information: channel quality information of the entire bandwidth        Sub-band CQI information: channel quality information of a partial bandwidth. This is channel information necessary for frequency-selective scheduling.        Multiple Input Multiple Output (MIMO)-related CQI information: channel quality information for use of multiple antennas        
The scheduling scheme and multi-antenna scheme that a base station desires to use, and/or the type of CQI information necessary for channel conditions of terminals, can be different for each base station. In other words, when the base station uses frequency-selective scheduling and a channel condition of a terminal is good, the terminal can be allocated a good sub-band if it transmits sub-band CQI information.
Currently, to transmit a control channel such as ACK/NACK information for downlink data and CQI information, which are not directly related to data transmission on the uplink, LTE allocates a particular resource block to a control channel as shown in FIG. 1A. In order to distinguish multiple terminals in the resource block, LTE uses/transmits different codes for the terminals. When a terminal transmits control information over allocated frequency resources 101, it is impossible to simultaneously transmit control information and packet data. This is because the simultaneous transmission of packet data and control information in the same transmission interval may increase a Peak to Average Power Ratio (PAPR) as it may not satisfy the single carrier characteristic. Therefore, in the interval where the terminal transmits packet data, a signal on a control channel (e.g., Physical Uplink Control Channel (PUCCH)) is transmitted using frequency resources for a data channel (e.g., Physical Uplink Shared Channel (PUSCH)) as shown in FIG. 1B. In other words, packet data, control information and reference signal are transmitted after undergoing time multiplexing in the same frequency resources 102.
FIG. 2 illustrates a method of transmitting control channels when data exists and when no data exists in a system having the channel structure for control information transmission, shown in FIG. 1.
It is assumed in FIG. 2 that a terminal transmits CQI every 10 ms (See CQI transmit time 202) over PUSCH/PUCCH 201. At 203 and 204, since there is no packet data transmission, i.e., since there is no transmission on PUSCH, the terminal transmits CQI through resource blocks at both ends allocated for control channels. At 205 and 206, since there is transmission data, the terminal transmits data and CQI together using the resources allocated for data transmission.
The transmission method of FIG. 2 is useful for the case where the CQI information is small in amount and occurs periodically. However, in the case where the amount of CQI information is large, even though resources are allocated, the terminal may not use the allocated resources at the CQI transmission times 205 and 206, increasing the resource waste. Since the CQI requiring the great amount of information (e.g., sub-band CQI and MIMO-related information) is generally transmitted only after downlink data is generated and only when there is downlink data to transmit, it is preferable to transmit the necessary CQI information by upper layer signaling only when necessary, without periodically transmitting it.
The most-direct possible method for this is a method in which the base station provides information on frequency resources for CQI transmission every time it determines that there is a need for the frequency resources. However, for this, the base station should send a new resource allocation message for scheduling, and sending signaling only for this purpose may cause signaling overhead.
A method may also be considered which transmits CQI only when the terminal has data to transmit over the uplink. However, since there is no direct relation between the uplink data transmission method and the CQI transmission method, there is a need for a detailed terminal's operation of transmitting data and CQI in association with each other, in order to realize the methods.